1. Field of the Invention
The present invention relates to an exercise apparatus and, more particularly, to an adjustable exercise apparatus that allows for variable amounts of resistances to be applied using weight resistance (e.g., iron plates), pneumatic resistance, or both weight and pneumatic resistances.
2. Description of the Related Art
Weight lifting for exercise and strength training commonly involves lifting iron weights. Typically, the weights are fixed to a bar (e.g., a barbell), are freely added to or removed from a weight-lifting bar (e.g., as with free weights), or are part of a weight stack in which the number of weight plates resisting movement of a handle or a bar can be varied. Examples of weight stack machines are disclosed in U.S. Pat. Nos. 6,447,430, 5,776,040, and 4,500,089. When users lift iron weights, the weights provide resistance to the exertion of muscular force. The resistance experienced by the user changes, however, depending upon the speed at which the concentric or eccentric movement of the weight occurs. For example, at the top of a concentric movement, the resistance often decreases as the weight lifter decelerates the weight.
Pneumatic exercise equipment has been developed in response to this shortcoming of weights. Such exercise equipment simulates the desired characteristics of a weight stack machine by permitting the weight lifter to quickly and easily increase or decrease the resistance. Moreover, pneumatic exercise equipment also provides a constant resistance because such machines do not have significant inertial effects. Consequently, pneumatic exercise equipment ensures full muscular effort throughout the stroke.
Pneumatic exercise equipment is typically configured similarly to weight stack equipment and therefore does not require, like free weights would, that the user balance the weight during each exercise repetition. Free weights also provide the user with greater freedom of movement than typical pneumatic exercise equipment, which requires the user to move a bar or handle along a predefined path. Accordingly, for many weight lifters, pneumatic exercise equipment does not provide the feel to which they are accustomed.